As the braking device of the railway vehicle, a disc brake excellent in braking performance is frequently used with increase in speed and size of a vehicle. In the disc brake, a brake disc is mounted on a wheel by being fastened with a bolt, a braking force due to frictional resistance is generated by a brake lining pushed against a sliding surface of the brake disc, and thus the rotation of the wheel is braked to regulate a speed of the vehicle.
FIGS. 1A and 1B are diagrams schematically illustrating a mounting structure of a typical railway vehicle brake disc onto a wheel; FIG. 1A illustrates a plan view of a ¼ circular portion in a front surface view; and FIG. 1B illustrates a cross-sectional view taken along the radial direction of a ½ circular portion. FIGS. 2A to 2C are schematic views illustrating a configuration of a railway vehicle brake disc of the related art; FIG. 2A illustrates a partial perspective view when viewed from a rear surface side; FIG. 2B illustrates a partial plan view in a rear surface view; and FIG. 2C illustrates a partial cross-sectional view taken along the radial direction.
As illustrated in FIGS. 1A and 1B and 2A to 2C, a brake disc 1 includes a donut-shaped disc section 2 having a sliding surface on a front surface 2a side. In a rear surface 2b of the disc section 2, a plurality of fin sections 3 is convexly provided in a radial pattern. A bolt hole 4 passing through the disc section 2 is formed almost at a central position in the radial direction in some of the plurality of fin sections 3.
A wheel 10 includes a boss section 11 pressed fit into an axle, a rim section 12 containing a wheel tread which comes into contact with a rail, and a plate section 13 which connects these sections. One set of two brake discs 1 is disposed so as to interpose the plate section 13 of a wheel 10 therebetween in a state where each front surface 2a faces outward; a bolt 15 is inserted into each bolt hole 4; and a nut 16 is fastened to each bolt 15. Thereby, the brake disc 1 is mounted on the wheel 10 in a state where a front end surface 3a of the fin sections 3 are in press contact with the plate section 13 of the wheel 10 over the entire area in the radial direction.
Here, in the case of a high speed railway vehicle such as the Shinkansen running at a speed exceeding 300 km/h, the brake disc 1 rotates integrally with the wheel 10 at a high speed during the running. Accordingly, the ambient air of the brake disc 1 is sucked from an inner peripheral side into a space between the brake disc 1 and the wheel 10, that is, a space surrounded by the disc section 2 and the fin section 3 of the brake disc 1 and the plate section 13 of the wheel 10, and discharged from an outer peripheral side (see solid arrows in FIGS. 2A to 2C). In short, a gas stream of the air is caused between the brake disc 1 and the wheel 10 during the running of the railway vehicle. The gas stream remarkably appears in a high speed running state of more than 300 km/h, and induces noises called aerodynamic noise. Therefore, it is necessary to reduce the aerodynamic noise in views of environmental concerns.
As a solution for such a request, for example, Patent Literature 1 discloses a brake disc in which a rib is added between neighboring fin sections along a circumferential direction, and the gas stream is suppressed by the rib. According to the brake disc disclosed in the above literature, the aerodynamic noise can be reduced to a desired level. However, a problem of lower cooling performance of the brake disc at the time of braking with suppression of the gas stream by the rib becomes apparent.
In addition, in a case where an emergency brake is used in the high speed running state, for example, as described in Patent Literatures 2 and 3, deformation of the brake disc associated with thermal expansion, and a stress load on a fastening bolt due to the deformation increase, and it becomes difficult to secure the durability of the brake disc and the bolt.